Individuals often wish to be cooled, especially in warm ambient temperatures. The desire to be cooled may arise indoors or out, while exercising, engaging in sports, driving, or being in an environment that is not comfortably cool. It may also be desirable to cool a portion of a user's body for medical reasons. Alternatively, in cold environments or perhaps to aid in recovering from an illness or injury, it can be beneficial to heat a portion of an individual's body.
It is known in the art to provide a cap to be worn by an individual that can provide some cooling. U.S. Pat. No. 5,365,607 to Benevento, for example, discloses a cap whose headband includes a plurality of tapered porous pads. The pads are wet with water and apparently produce a cooling effect to the user's head as the water evaporates.
U.S. Pat. No. 3,029,438 to Henschel discloses a water-cooled cap in which an inner aluminum strip contacts the wearer's head, and is contacted with at least one water absorbent sponge strip over-covered by a fabric. The sponge material is moistened and as the water evaporates the aluminum strip cools, thus cooling the wear's head.
Of course other caps may be worn to warm a user. However typically the same cap is not adapted for cooling and for warming the user.
U.S. Pat. No. 4,130,902 to Mackenroth discloses a cooling hat band that includes an outer support band, an inner absorbent band, a wicking element and a water reservoir. Reservoir water moves along the wicking element to the absorbent band, whence it evaporates, passing through holes in the support band. The evaporative effect is said to remove heat from the headband, and thus from the wear's forehead.
However, not all individuals like to wear caps, and participation in some sports, e.g. bicycling, may dictate that another type of headgear be worn, a helmet for example. Thus, several attempts have been made in the prior art to improve upon a basic cooling band, such as a tennis player might wear around the forehead. For example, U.S. Pat. No. 4,742,581 to Rosenthal discloses a laminated cooling band. The band comprises a skin-contacting air pervious heat conductive layer edge-connected to an air pervious fabric that is moistened with water exposed to ambient air. This device is said to cool the wearer as water evaporates from the outer fabric. However, as is typical with many prior art devices, evaporative cooling is dependent upon ambient air motion. If the wearer is stationary, the efficiency of evaporative cooling decreases. Further, Rosenthal's band does not appear to provide an option to heat rather than cool the user.
A substantially new type of personal cooling device is disclosed in U.S. Pat. No. 5,802,865 to Strauss (1998). The Strauss device disposes self-supporting heat sink around the user's neck (or other body portion to be cooled). Body heat is transferred to the heat sink and is actively carried away by fan-induced flow of moistened air. Although the Strauss device works admirably well, it is mechanically complex to fabricate and provides little cooling unless the fan is operating and the device is replenished with liquid. Further, it is difficult to precisely control the extent of cooling. Finally, like many prior art devices, Strauss' device cools but cannot heat.
A prior art device that is able to heat or cool is shown in FIG. 1A. FIG. 1A depicts a prior art Peltier thermoelectric device 2 coupled to a source of operating potential 4. Device 2 comprises two dissimilar electrical conducting materials (often metals) that form a junction. When device 2 is coupled to power source 4, electrical current "i" flows in the direction shown. Interestingly, the temperature at the device junction rises or falls, relative to ambient temperature, depending upon polarity of i. For example, if the two metals are copper and bismuth, the copper-bismuth junction temperature will increase when positive charge flows from the bismuth to the copper metal. Thus, the bias configuration of FIG. 1A will cause surface 6 of device 2 to be warmer by AT degrees relative to surface 8. If surface 8 is at ambient temperature, perhaps 20.degree. C., then surface 6 will attempt to reach perhaps 23.degree. C.
On the other hand, if bias polarity is reversed as shown in FIG. 1B, junction temperature will decrease when the current flow is from the bismuth to the copper metals. Thus, surface 6 will now attempt to be cooler than surface 8 by .DELTA.T.
Conductors other than bismuth and copper may be used. More modern Peltier thermoelectric devices 2 use semiconductor materials, materials that advantageously are good conductors of electricity but poor conductors of heat. Such devices often comprise bismuth telluriude that is heavily doped to create n-type and p-type semiconductor material. A number of such p-type and n-type materials are formed as thermocouple pairs that are sandwiched between ceramic plates and are electrically series-coupled to a power source 4.
Unfortunately even modern Peltier thermo-voltaic devices 2 have not lent themselves to portable or self-contained cooling and/or heating applications because the operating potentials and currents are large. Typically operating potential for source 4 might be 15 VDC, and the magnitude of current i is perhaps 6 A. While an automobile battery could power such devices for a short time, such batteries hardly lend themselves to portability in a personal cooling/heating application. Understandably this range of power consumption has excluded Peltier thermo-voltaic devices from self-contained battery operated applications.
An additional problem with Peltier thermo-voltaic devices is that as soon as the operating potential is removed (e.g., current flow is halted), the thermal effect tends to reverse. Thus in FIG. 1A, if surface 6 of device 2 was intentionally made warmer, turning off or removing the power source 4 would cause surface 6 to become cooler (and surface 8 to try to become warmer). In a personal cooling/heating device application (assuming the problem of provide sufficient operating power were overcome), this reversal effect is most unpleasant. A person trying to warm up with a Peltier thermo-voltaic device must remove the device almost instantly upon turning off the power source to avoid being cooled. Similarly, a person trying to become cooler with such a device could suddenly find themselves being warmed upon turning off the power source.
Thus, there is a need for a self-contained personal device that promotes efficient cooling or heating. If worn about the user's neck, such device should not require headgear. Further, such device should be useable on other portions of the user's body, the forehead, for example. Preferably, such device should be simple to implement mechanically, offer precise temperature control, and be useable for cooling or for heating. Such device should be simple to use and wear, and should provide cooling or heating for several hours without replenishment of the energizing source.
The present invention provides such a device.